This presentation introduces the key concepts at the foundation of DDS, the data distribution service for real-time systems. Wether you are a new to DDS or a relatively experienced user, you'll find this presentation a good source of information.

1. The Data Distribution Service
[For Real-Time Systems]
OpenSplice DDS
Angelo CORSARO, Ph.D.
Chief Technology Officer
OMG DDS Sig Co-Chair
PrismTech
angelo.corsaro@prismtech.com

2. OpenSplice DDS
Background

3. Data Distribution Service
For Real-Time Systems
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☐ Introduced in 2004 to address
the Data Distribution Real-Timeliness Scale
challenges faced by a wide
class of Defense and
Aerospace Applications
OpenSplice DDS
Key requirement for the
Parallelism Determinism Throughput, Availability Scalability, Persistence, Security
☐
standard were to deliver very Systemic
Signal
Data Real-Time Information
Near Real-Time Fault-
Tolerant Information
Complex Information
high and predictable
Processing Processing Management
Processing Processing
performance while scaling
from embedded to ultra- Parallel Systems Distributed Systems
large-scale deployments

4. Data Distribution Service
For Real-Time Systems
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☐ Recommended by key Real-Timeliness Scale
administration worldwide,
e.g. DoD, MoD, EUROCAE,
etc.
OpenSplice DDS
Widely adopted across
Parallelism Determinism Throughput, Availability Scalability, Persistence, Security
☐
several different domains, Systemic
Signal
Data Real-Time Information
Near Real-Time Fault-
Tolerant Information
Complex Information
e.g., Automated Trading,
Processing Processing Management
Processing Processing
Simulations, SCADA,
Telemetry, etc. Parallel Systems Distributed Systems

5. Some Use Cases
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Integrated Modular Vetronics Training & Simulation Systems Naval Combat Systems
OpenSplice DDS
Air Traffic Control & Management Large Scale SCADA Systems High Frequency Auto-Trading

6. Standards: What For?
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Common “Language”
Data Model +
OpenSplice DDS
QoS Requirements
Interoperability
DDSI Wire Interoperability

7. OpenSplice DDS
DDS
Application
API Standard
Standards: What For?
Portability
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8. OpenSplice DDS
D
D
BaS ics

9. Data Distribution Service
For Real-Time Systems
DDS provides a Topic-Based Publish/
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Subscribe abstraction based on: Data
Reader
Data
Writer
☐ Topics: data distribution subject’s
OpenSplice DDS
Data
Reader
Data TopicD
Writer
DataWriters: data producers
TopicA
☐
Data
TopicB Reader
Data
Writer
☐ DataReaders: data consumers TopicC
...
Data Data
Writer Reader
DDS Global Data Space

10. Data Distribution Service
For Real-Time Systems
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☐ DataWriters and DataReaders Data
Reader
are automatically and
Data
Writer
dynamically matched by the
OpenSplice DDS
Data
Reader
Data TopicD
DDS Dynamic Discovery Writer
TopicA
Data
TopicB Reader
Data
☐ A rich set of QoS allows to Writer
TopicC
...
control existential, temporal, Data Data
and spatial properties of data Writer Reader
DDS Global Data Space

11. DDS Topics
☐ A Topic defines a class of “TVehicleDynamics”
streams
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Name
☐ A Topic has associated a user
defined extensible type and a Topic
Typ
set of QoS policies
S
DURABILITY,
Qo
OpenSplice DDS
e
DEADLINE,
☐ The Topic name, type and QoS VehicleDynamics
PRIORITY,
defines the key functional and …
non-functional invariants
struct VehicleDynamics {
IDL
☐ Topics can be discovered or long vid;
locally defined long x; long y;
long dx; long dy;};
#pragma keylist VehicleDynamics vid

12. Topic Instances
☐ Each unique key value
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identifies a unique stream
of data vid =701
DDS not only
vid =809 struct VehicleStatus {
☐ Topic
long vid;
OpenSplice DDS
long x; long y;
long dx; long dy;};
demultiplexes “streams”
#pragma keylist VehicleStatus vid
vid =977
but provides also lifecycle Instances Instances
information
☐ A DDS DataWriter can
write multiple instances

13. OpenSplice DDS
Anatomy of a DDS Application
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14. Anatomy of a DDS Application
[Scala API]
Domain
Domain
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val dp = DomainParticipant(domainId)
Participant
Publisher
Topic
Subscriber
OpenSplice DDS
DataWriter
DataReader

15. Anatomy of a DDS Application
[Scala API]
Domain
Domain
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val dp = DomainParticipant(domainId)
Participant
Session
// Create a Publisher / Subscriber
Publisher
Topic
Subscriber
OpenSplice DDS
val pub = Publisher(dp)
val sub = Subscriber(dp)
// Create a Topic
val topic = Topic[VehicleDynamics](dp, “TVehicleDynamics”)
DataWriter
DataReader

16. Anatomy of a DDS Application
[Scala API]
Domain
Domain
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val dp = DomainParticipant(domainId)
Participant
Session
// Create a Publisher / Subscriber
Publisher
Topic
Subscriber
OpenSplice DDS
val pub = Publisher(dp)
val sub = Subscriber(dp)
// Create a Topic
val topic = Topic[VehicleDynamics](dp, “TVehicleDynamics”)
Reader/Writers for User Defined for Types DataWriter
DataReader
// Create a DataWriter/DataWriter
val writer = DataWriter[TempSensor](pub, topic) Reader/Writer for
val reader = DataReader[TempSensor](sub, topic)
application defined
Topic Types

17. Anatomy of a DDS Application
[Scala API]
Domain
Domain
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val dp = DomainParticipant(domainId)
Participant
Session
// Create a Publisher / Subscriber
Publisher
Topic
Subscriber
OpenSplice DDS
val pub = Publisher(dp)
val sub = Subscriber(dp)
// Create a Topic
val topic = Topic[VehicleDynamics](dp, “TVehicleDynamics”)
Reader/Writers for User Defined for Types DataWriter
DataReader
// Write data
val data = new VehicleDynamics(101, 131, 107, 7, 5)
writer write data
Reader/Writer for
// But you can also write like this... application defined
writer ! data Topic Types
// Read new data and print it on the screen
(reader read) foreach (prinln)

18. Anatomy of a DDS Application
[DDS C++ API 2010]
Domain
Domain
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auto dp = DomainParticipant(domainId);
Participant
Session
// Create a Publisher / Subscriber
Publisher
Topic
Subscriber
OpenSplice DDS
auto pub = Publisher(dp);
auto sub = Subscriber(dp);
// Create a Topic
auto topic = Topic<VehicleDynamics>(dp, “TVehicleDynamics”);
Reader/Writers for User Defined for Types DataWriter
DataReader
// Create a DataWriter/DataWriter
auto writer = DataWriter<TempSensor>(pub, topic); Reader/Writer for
auto reader = DataReader<TempSensor>(sub, topic);
application defined
Topic Types

19. Anatomy of a DDS Application
[DDS C++ API 2010]
Domain
Domain
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auto dp = DomainParticipant(domainId);
Participant
Session
// Create a Publisher / Subscriber
Publisher
Topic
Subscriber
OpenSplice DDS
auto pub = Publisher(dp);
auto sub = Subscriber(dp);
// Create a Topic
auto topic = Topic<VehicleDynamics>(dp, “TVehicleDynamics”);
Reader/Writers for User Defined for Types DataWriter
DataReader
// Write data
writer.write(VehicleDynamics(101, 131, 107, 7, 5)); Reader/Writer for
// But you can also write like this...
writer << VehicleDynamics(101, 131, 107, 7, 5);
application defined
Topic Types
// Read new data
auto data = reader.read();

20. OpenSplice DDS
QoS

21. QoS Model
☐ QoS-Policies control local and
end-to-end properties of DDS
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entities
Type Matching
QoS matching
QoS QoS QoS QoS QoS QoS QoS
☐ Local properties controlled by Topic
QoS are related resource usage Publisher
Name
Subscriber
... DataWriter writes Type reads DataReader
...
☐ End-to-end properties
OpenSplice DDS
...
controlled by QoS are related
DomainParticipant DataWriter writes Type reads DataReader DomainParticipant
Name
to temporal and spatial aspects
Topic
of data distribution QoS QoS QoS
☐ Some QoS-Policies are
matched based on a Request
vs. Offered Model thus QoS-
enforcement

22. QoS Policies
[T: Topic] [DR: DataReader] [DW: DataWriter] [P: Publisher] [S: Subscriber] [DP: Domain Participant]
QoS Policy Applicability RxO Modifiable
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USER_DATA DP, DR, DW N Y
TOPIC_DATA T N Y Configuration
GROUP_DATA P, S N Y
DURABILITY T, DR, DW Y N
OpenSplice DDS
DURABILITY T, DW N N
SERVICE Data Availability
HISTORY T, DR, DW N N
PRESENTATION P, S Y N
RELIABILITY T, DR, DW Y N
PARTITION P, S N Y
Data Delivery
DESTINATION T, DR, DW Y N
ORDER
LIFESPAN T, DW N Y

23. QoS Policies
[T: Topic] [DR: DataReader] [DW: DataWriter] [P: Publisher] [S: Subscriber] [DP: Domain Participant]
QoS Policy Applicability RxO Modifiable
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DEADLINE T, DR, DW Y Y
LATENCY T, DR, DW Y Y
BUDGET Temporal/
TRANSPORT T, DW N Y Importance
PRIORITY Characteristics
OpenSplice DDS
TIME BASED DR N Y
FILTER
OWNERSHIP T, DR, DW Y N
OWNERSHIP DW N Y Replication
STRENGTH
LIVELINESS T, DR, DW Y N Fault-Detection

24. Temporal Properties
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TimeBasedFilter Deadline
[Inbound]
OpenSplice DDS
Throughput LatencyBudget Latency
[Outbound]
TransportPriority

25. Data Availability
History
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Data
OpenSplice DDS
Lifespan Durability
Availability
Ownership
Ownership
Strength

26. OpenSplice DDS
Partition
Data Delivery
Reliability
Presentation
Data Delivery
Order
Destination
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27. Setting QoS Policies
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C++
// Setting Partition QoS-Policy on Publisher
qos::PublisherQos pubQos;
pubQos << policy::Partition("Partition");
Publisher pub(dp, pubQoS);
OpenSplice DDS
// Setting various QoS-Policy on a Topic
qos::TopicQos tqos;
tqos << policy::Reliability::Reliable()
<< policy::Durability::Transient()
<< policy::History::KeepLast(5);
Topic<VehicleDynamics> topic(dp,"Partition", tqos);

28. Data Reader/Writer Caches
OpenSplice DDS

29. DDS Model
Topic Instances
DataWriter DataReader DataReader
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... ... ... ...
...
...
...
...
...
...
...
...
...
OpenSplice DDS
DataWriter Cache DataReader Cache DataReader Cache
Writer History Reader History
network

30. DDS Model
DataWriter DataReader DataReader
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... ... ... ...
...
...
...
...
...
...
...
...
...
OpenSplice DDS
DataWriter Cache DataReader Cache DataReader Cache
QoS Policies
‣ History
‣ Destination Order
‣ Presentation network
‣ Partition
‣ Time Based Filter QoS Policies
‣ Ownership ‣ Reliability ‣ Durability
‣ History ‣ Transport Priority
‣ Latency Budget ‣ Time Based Filter

31. Dynamic View of a Stream
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OpenSplice DDS
...
Stream: Set of samples written over
time for a given topic instance.

32. Dynamic View of a Stream
Assumptions:
Reader History = KeepLast (n)
WriterHistory = KeepLast (m)
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Writer History
OpenSplice DDS
...
Stream: Set of samples written over
time for a given topic instance.

33. Dynamic View of a Stream
Assumptions:
Reader History = KeepLast (n)
WriterHistory = KeepLast (m)
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Samples ‘on
Writer History the wire’
OpenSplice DDS
...
Stream: Set of samples written over
time for a given topic instance.

34. Dynamic View of a Stream
Assumptions:
Reader History = KeepLast (n)
WriterHistory = KeepLast (m)
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Samples ‘on
Writer History the wire’ Reader History
OpenSplice DDS
...
Stream: Set of samples written over
time for a given topic instance.

35. Dynamic View of a Stream
Assumptions:
Reader History = KeepLast (n)
WriterHistory = KeepLast (m)
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Samples ‘on
Writer History the wire’ Reader History
‘Past’ Samples
OpenSplice DDS
...
Stream: Set of samples written over
time for a given topic instance.

36. Eventual View of a Stream
Assumptions (Default Settings):
Reader History = KeepLast (1)
WriterHistory = KeepLast (1)
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Writer History
Reader History ‘Past’ Samples
OpenSplice DDS
Stream: Set of samples written over
time for a given topic instance.

37. Eventual View of a Stream
Assumptions:
Reader History = KeepLast (n) with n > 1
WriterHistory = KeepLast (1)
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Writer History Reader History
‘Past’ Samples
OpenSplice DDS
Stream: Set of samples written over
time for a given topic instance.

38. Eventual View of a Stream
Assumptions:
Reader History = KeepLast (n) with n > 1
WriterHistory = KeepLast (m) with n > m > 1
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Writer History Reader History
‘Past’ Samples
OpenSplice DDS
Stream: Set of samples written over
time for a given topic instance.

39. Reading Data Samples
☐ Samples can be read from the Data Reader History Cache
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☐ The action of reading a sample is non-destructive. Samples are
not removed from the cache
OpenSplice DDS
DataReader DataReader
... read ...
DataReader Cache DataReader Cache

40. Taking Data Samples
☐ Samples can be taken from the Data Reader History Cache
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☐ The action of taking a sample is destructive. Samples are
removed from the cache
OpenSplice DDS
DataReader DataReader
... ...
take
DataReader Cache DataReader Cache

41. Read vs. Take
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☐ The read operation should always be access the latest
know value for topics that represent distributed state
OpenSplice DDS
☐ The take operation should be used to get the last
notification from a topic that represent an event

42. Data Selectors
OpenSplice DDS

43. Cherry Picking in DDS
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☐ DDS provides some very flexible mechanisms for
selecting the data to be read:
OpenSplice DDS
☐ Data Content
☐ Data Status
☐ These mechanisms are composable

44. Content-Based Data Selection
OpenSplice DDS

45. Filters and Queries Application
☐ DDS Filters allow to control what gets
into a DataReader cache
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Query
☐ DDS Queries allow to control what gets
out of a DataReader cache DataReader
OpenSplice DDS
☐ Filters are defined by means of
...
ContentFilteredTopics
...
...
...
☐ Queries operate in conjunction with DataReader Cache
read operations
Filter
☐ Filters and Queries are expressed as SQL
where clauses

46. Filters
[Scala API]
struct VehicleDynamics {
long vid;
long x; long y;
long dx; long dy;};
#pragma keylist VehicleStatus vid
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/**
** NOTE: The Scala API if not provided with DP/Sub/Pub assumes default domains and
** default partition.
**/
// Create a Topic
val topic = Topic[VehicleDynamics](“TVehicleDynamics”)
OpenSplice DDS
// Define filter expression and parameters
val filter = “x < %0 AND y < %1”
val params = List(“200”, “300”)
// Define content filtered topic
val cftopic =
ContentFilteredTopic[VehicleDynamics](“CFTVehicleDynamics”, topic, filter, params)
// Create a DataReader for the content-filtered Topic
val reader =
DataReader[VehicleDynamics](cftopic)

47. QueryAPI 2010] struct VehicleDynamics {
[DDS C++ long vid;
long x; long y;
long dx; long dy;};
#pragma keylist VehicleStatus vid
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// Define the query and the parameters
OpenSplice DDS
std::vector<std::string> p;
p.push_back("100");
p.push_back("100");
dds::core::Query q("x < %0 AND y < %1", p.begin(), p.end());
auto data = reader
.selector()
.filter_content(q)
.read();

48. Instances
☐ DDS provides a very efficient way of reading data belonging to a
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specific Topic Instance
☐ Obviously, one could use queries to match the key’s value, but this
is not as efficient as the special purpose instance selector
OpenSplice DDS
// C++
auto data = reader
.selector()
.instance(handle)
.read();
// Scala
val data = reader read(handle)

49. State-Based Selection
OpenSplice DDS

50. Sample, Instance, and View State
☐ The samples included in the DataReader cache have associated
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some meta-information which, among other things, describes the
status of the sample and its associated stream/instance
☐ The Sample State (READ, NOT_READ) allows to distinguish between
OpenSplice DDS
new samples and samples that have already been read
☐ The View State (NEW, NOT_NEW) allows to distinguish a new
instance from an existing one
☐ The Intance State (ALIVE, NOT_ALIVE_DISPOSED,
NOT_ALIVE_NO_WRITERS) allows to track the life-cycle transitions of
the instance to which a sample belongs

51. State Selector in Action
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// Read only new samples
auto data = reader
C++ Scala
.selector() // Read only new samples
.filter_state(status::DataState::new_data()) val data = reader read
.read()
OpenSplice DDS
// Read any samples from live instances
// Read any samples from live instances val data = reader read(SampleSelector.AnyData)
auto data = reader
.selector()
.filter_state(status::DataState::any_data())
.read()

52. Putting all Together
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☐ Selectors can be composed in a flexible and
expressive manner
OpenSplice DDS
C++
auto data = reader
! .selector()
.instance(handle)
! ! .filter_state(status::DataState::new_data())
! ! .filter_content(q)
.read();

53. OpenSplice DDS
S
D
D
tandard

54. DDS Standard Ecosystem
Application Application
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2012 API 2012
DDS RMI DDS RMI
2012 2010 2010 2012
ANSI C ISO C++ Java-5 Scala
OpenSplice DDS
2004 2010 2010 201x
Security
Security
X-Types
X-Types
DDS 2004
Wire Protocol
DDSI-RTPS network DDSI-RTPS
2006 2006

55. Concluding Remarks
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☐ The Data Distribution Service for Real-Time Systems
provides a powerful and feature-rich topic-based
publish/subscribe abstraction
OpenSplice DDS
☐ This technology is widely used in mission and business
critical systems and it being swiftly adopted in data-
centric/big-data systems

56. References
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OpenSplice | DDS Escalier
¥ #1 OMG DDS Implementation ¥ Fastest growing JVM Language ¥ Scala API for OpenSplice DDS
¥ Open Source ¥ Open Source ¥ Open Source
¥ www.opensplice.org ¥ www.scala-lang.org ¥ github.com/kydos/escalier
OpenSplice DDS
[C++] [Java] DDS-PSM-Cxx 2010
¥ Simple C++ API for DDS ¥ DDS-PSM-Java for OpenSplice DDS ¥ DDS-PSM-Cxx API Standard
¥ Open Source ¥ Open Source ¥ Open Source
¥ code.google.com/p/simd-cxx ¥ github.com/kydos/simd-java ¥ github.com/kydos/dds-psm-cxx

57. :: Connect with Us ::
¥opensplice.com ¥forums.opensplice.org
¥@acorsaro
¥opensplice.org ¥opensplicedds@prismtech.com ¥@prismtech
OpenSplice DDS
¥ crc@prismtech.com
¥sales@prismtech.com
¥youtube.com/opensplicetube ¥slideshare.net/angelo.corsaro